1. C++ Basics
Lecture 2

2. Variables and Assignments
Programs manipulate data such as numbers and letters
C++ uses variables to name & store data
Variable
num1
Memory
num2
123
456
grade B
Name
(Identifier)
Value

3. Variables and Assignments
Variable Declarations
Syntax:
Type_Name Variable_Name1, Variable_Name_2, …;
Example:
int count, total;
double price;
All variables must be declared before they are used in the program.

4. Variables and Assignments
#include <iostream>
using namespace std;
int main()
{ int number_of_bars;
double one_weight, total_weight;
cout<< "Enter the number of candy bars in a package\n";
cout<< "and the weight in ounces of one candy bar.\n";
cout<< "Then press return.\n";
cin>> number_of_bars;
cin>> one_weight;
total_weight = one_weight * number_of_bars;
cout<< "Total weight is " <<total_weight << " ounces.\n";
return 0; }

5. Variables and Assignments
Names: Identifiers
Begin with a letter or underscore
Remaining characters must be
Letters or
Digits or
Underscore 
sum
Big_Bonus  3X 
_address 
%change 
program1.cpp 
_3X 
price-1 
total5* 

6. Variables and Assignments
Notes on Identifiers
C++ is case sensitive
Average
AVERAGE
average
Use meaningful names
Keywords/reserved words
int
double

7. Variables and Assignments
Assignment Statements
Syntax:
Variable = Expression ;
Examples:
distance = speed_rate * time;
count = count + 2;
weight = 35;

8. Variables and Assignments
Initializing variables
Syntax:
Type Variable_Name_1 = Expression_for_value_1,
Variable_Name_2 = Expression_for_value_2,..;
Type Variable_Name_1 ( Expression_for_value_1),
Variable_Name_2 ( Expression_for_value_2),..;
Examples:
int count = 0, max = 555;
int count(0), max(555);

9. Input and Output Input stream Output stream
The stream of input that is being fed into the computer for the program to use
cin ( cin>> number_of_bars; )
Output stream
The stream of output generated by the program
cout (cout<< "Enter the number of candy bars.\n";)

10. Input and Output Input Using cin cin >> grade1;
Syntax:
cin >> Variable_1 >> Variable_2 >>…;
Examples:
cin >> number >> size;
cin >> grade1
>> grade2;
cin >> grade1;
cin >> grade2;

11. Input and Output Output Using cout Syntax:
cout << Variable_or_string_1 << Variable_or_string_2 << … ;
Examples:
cout << number << size;
cout << “Hello \n”;

12. Input and Output Include directive Using directive
Namespaces (collection of names)
# include <iostream>
using namespace std;

13. Input and Output Escape Sequences
The backslash \ preceding a character tells the compiler that the sequence following the \ doesn’t have the same meaning as the character appearing by itself.
New_line \n
Horizontal tab \t
Alert \a
Backslash \\
Double quote \”
Others: v, b, r, ?, :, \000, \xhhh

14. Input and Output New line & Blank lines
cout<< “\n”;
cout<< endl;
If you could include the \n at the end of a longer string, then use \n.
If the \n would appear by itself as the short string “\n”, then use endl instead.

15. Input and Output Formatting numbers with a decimal point
double price = 84.50;
cout << “The price is $” << price<<endl;
The price is $84.5
The price is $
The price is $84.50
The price is $ e01

16. Input and Output Magic Formula cout.setf (ios::fixed);
cout.setf(ios::showpoint);
cout.precision(2);

17. Input and Output Line Breaks in I/O
You can keep input and output on the same line by omitting the \n or endl at the end of the last prompt line.
Example:
cout<< “Enter the cost per person: $”;
cin >> cost_per_person;
Enter the cost per person: $5.40

18. Lab Exercise
Your local department store is having its annual sale. Write a program that calculates the sale price for items in the store. The program should prompt the user for the original price and the discount (10%, 25%, etc.)

19. Lab Exercise include <iostream> using namespace std; int main()
{ double discount, price;
cout<<"Enter the price of the item: $";
cin>> price;
cout<<"Enter the discount for the this item: %";
cin>> discount;
price = price - (price * discount/100);
cout.setf (ios::fixed);
cout.setf(ios::showpoint);
cout.precision(2);
cout<<"\nThe sale price for your item is: $"<< price;
cout<<endl;
return 0; }

20. Lab Exercise
Write a Program to convert a temperature in degrees Fahrenheit to degree Celcius.
Data Requirement
Problem input
int Fahrenheit
Problem OutPut
Float Celcius
Formula
Celcius = (5/9) * (faherenheit – 32)

21. Lab Exercise
write a Program to read two data items and print their sum, difference, product, and quotient.
2. Write a program that reads in the length and width of a rectangular yard and the length and width of a rectangular house situated in the yard. Your program should compute the time required to cut the grass at the rate of 2 square meters per second